Endothelial dysfunction is a disruption of the normal biochemical processes carried out by the endothelium, which is a cell group that lines the inner surface of all blood vessels, including arteries and veins. The normal function of the endothelial cells is to produce or release substances that control the biological characteristics of the blood vessels, including the dimension, elasticity, permeability and reactivity. Since impairment of the vascular endothelial function is found in early stages of atherosclerosis, it is possible to treat the atherosclerosis earlier by detecting the impairment of the vascular endothelial function. Endothelial dysfunction is thought to be a key event in the development of atherosclerosis and can predate clinically obvious vascular pathology by many years. Endothelial dysfunction has been shown to be of prognostic significance in predicting vascular events, including stroke and heart attacks.
A key feature of endothelial dysfunction is the inability of the arteries to dilate fully in response to an appropriate stimulus. This can be tested by a variety of methods including intra-arterial administration of various vasoactive agents, localized heating of the skin and temporary arterial occlusion by inflating a blood pressure cuff to high pressures. These techniques are thought to stimulate the endothelium to release nitric oxide (NO) and other agents, which diffuse into the surrounding vascular smooth muscles causing vasodilation. Flow-mediated dilation (FMD) is a non-invasive method for assessing vascular endothelial function by inducing reactive hyperemia with an occlusive cuff and by measuring arterial diameter with an ultrasonic probe. Reactive hyperemia is a transient increase in blood flow that takes place following a brief period of arterial occlusion and the subsequent release thereafter. The flow mediated dilation is a reaction in which an increased arterial blood flow stimulates the vascular endothelium of the artery concerned (typically the brachial artery), thus secreting vascular endothelium-derived relaxing factors that dilate the blood vessels, with a resulting increase in the diameter of the artery. When the vascular endothelial function is impaired the relaxing factors are secreted at a smaller quantity, which results in a smaller increase in arterial diameter. Thus, the vascular endothelial function can be assessed by measuring the extent of the diameter change of the artery following the arterial occlusion and comparing it to reference values
Current methods to assess the endothelial function non-invasively use ultrasound to measure the FMD of the limb artery after the release of the temporary occlusion. However, the use of ultrasound probes poses problems for assessment of the vascular endothelial functions. Specifically, in presently used methods, the ultrasound measurements may be poorly reproducible since the technique is highly operator-dependent with regard to the positioning of the probe on the patient. Further, since the prior methods and systems require a trained technician to manually locate the blood vessel within the patient limb and simultaneously integrate the functions of the blood pressure cuff and the ultrasound probe, testing typically takes place in a research environment and is not widely used as a clinical tool.